Dr. Tim Johnson Explains Anthrax Tests

B O S T O N, Oct. 19

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Cultures — Culturing, or growing, anthrax bacteria is relatively simple, but does take some time. First the sample is plated, or placed, onto a lab petri dish containing a solid layer of gelatin, called agar, which contains nutrients for the bacteria to grow. Once plated, it takes 18 to 24 hours before the bacteria have grown enough to be analyzed. Scientists then study the bacteria that have grown on the plates.

PCR: Polymerase Chain Reaction — PCR allows scientists to amplify, or create copies, of small amounts of anthrax DNA into quantities large enough to analyze. The process only amplifies the specific DNA that you are looking for. This test can be done quickly in the field to determine if anthrax is present, and also again more thoroughly in the lab to determine if the bacteria contains specific genes, such as ones that might make the bacteria antibiotic-resistant.

Antibody tests — These tests indicate if your body has begun to fight off infection. One such test, sometimes called an ELISA, indicates if your body has produced antibodies against the anthrax bacteria. When you become infected with anything your body produces antibodies that help fight off the infection. If you have antibodies against the anthrax bacteria, and you were never exposed to it before, it would indicate that you are infected.

Microscopy — Anthrax bacteria have many distinguishing physical characteristics that scientists use to identify them from other types of bacteria under the microscope. For example, the anthrax are shaped like small rods, are non-motile, meaning they do not move around on their own, and are can be stained by certain dyes.

DNA fingerprinting — This test is usually done after all the others to find out the specific type of anthrax bacteria involved. By closely scrutinizing the bacteria's DNA, scientists can determine if two anthrax samples originate from the same strain. For fingerprinting, labs use PCR technology as well as other genetic techniques to study bacterial genes. Each bacterium has its own unique DNA fingerprint. By sequencing certain genes scientists can compare samples to an existing library of anthrax bacteria sequences. Figuring out where a bacterium came from can very difficult, especially if it turns out to be a strain commonly found in research institutions.